First flight - almost perfect

I flew my RV-8 for the first time today. Actually, I did two very short flights. Yea! Everything went great except one of my cylinders (#4) isn't doing what it's supposed to.

I'm really glad my VM-1000C stores data at 6-second intervals. Here's what happened on the second flight. Results were similar (almost identical, in fact) for both flights, except the #4 CHT got a little hotter on the first flight because I waited longer (higher altitude) to make the initial power reduction.

During the run-up (1800 RPM), EGT #4 was about 70F higher than the rest of them. Runup EGTs (in numerical order) were 1240, 1246, 1238, and 1312.

During and just after takeoff (at 2700 RPM, 29.1" Hg.), EGT #4 climbed to almost 300F higher than the other 3 cylinders. Initial climb EGTs (in numerical order) were 1272, 1264, 1276, 1558.

After engine power reduction (to 2400 RPM, 24" Hg.), EGT #4 started to decrease immediately. However, it remained higher than the other three until approach for landing four minutes later. Just before the power reduction for final approach, EGT #4 was about 130F higher than the rest of them. In numerical order, we have 1178, 1206, 1204, 1412.

Now let's talk about CHTs. #4 is definitely the hottest, #1 is the coolest, and #2 and #3 are about equal. #4 peaked two minutes after the initial power reduction. At that point, the CHTs (in numerical order) were 350, 376, 382, 420.

So it appears that at high power settings, I have high EGT and high CHT on #4. The Sky Ranch Engineering Manual seems to suggest a partially plugged fuel injector nozzle or an induction leak on that cylinder. The engine idles fine and the mag check is fine. It also shuts down normally. All other engine parameters are normal.

Where should I start? Induction or injector nozzle? How would I go about finding an induction leak if there were one?

Thanks.

-Geoff

RV-8
Mattituck TMX-IO360 (vertical induction) with two P-mags.

[airguy]

My first suspicion would be the injector nozzle, assuming a small bit of debris was in the line and found itself a nice little home to lodge into. I think you're on the right track, though - certainly sounds like one lean cylinder.

Are you breaking in a new engine, or does this one already have time on it? You could get to a decent altitude and pull the mixture into LOP territory, even for just a few seconds, and the EGT's will tell you a story.

Originally Posted by airguy

My first suspicion would be the injector nozzle, assuming a small bit of debris was in the line and found itself a nice little home to lodge into. I think you're on the right track, though - certainly sounds like one lean cylinder.

Are you breaking in a new engine, or does this one already have time on it? You could get to a decent altitude and pull the mixture into LOP territory, even for just a few seconds, and the EGT's will tell you a story.

New engine. Now that I know the plane flies, I don't want to do much screwing around with the engine (after fixing this issue, of course) before I do the high power break in.

-Geoff

[dan]

It's not likely an induction leak. An induction leak would probably appear at LOWER power settings.

I agree with airguy. Check everything on #4 from the flow divider to the cylinder. Make sure the tubing is clear, make sure the injector/restrictor are clean & clear.

Oh...and congrats on your first flight!!! Be safe, get the squawks ironed out, and it only gets better from here...

[scard]

I thought it wasn't good form to talk about absolute EGTs. An EGT could be just about anything (within metallurgic limits) and be fine. It sounds to me like a basic cooling imbalance. Work on getting the CHT down on that cylinder and you'll see a decrease in the EGT as well, no? Of course assuming the injectors are balanced which is very easy to test with a flow test.

[airguy]

Originally Posted by dan

It's not likely an induction leak. An induction leak would probably appear at LOWER power settings.

Unless it's a MASSIVE induction leak - in which case it wouldn't be idling fine as you indicated, it would be loping on 3 cylinders at idle. My money is on the nozzle.

[airguy]

Originally Posted by scard

Work on getting the CHT down on that cylinder and you'll see a decrease in the EGT as well, no?

In a word - no. CHT does not drive EGT, it's the other way around (mostly). If the mixture is lean in that cylinder, no amount of cooling is going to bring the EGT down to comparable with the correct mix. You can increase cooling all you want to get CHT down, but it's still running lean and the EGT will be high. A flow test should confirm it, but in this case with a new engine and break-in being needed immediately, you don't have time for lengthy diagnostics.

And you're basically right about absolute EGT numbers - it's the relative numbers that are worthwhile to pay attention to. In this case, it's obvious #4 is way above the other 3, the variation is all that you really need to know, not the absolute magnitude.

Originally Posted by dan

It's not likely an induction leak. An induction leak would probably appear at LOWER power settings.

I agree with airguy. Check everything on #4 from the flow divider to the cylinder. Make sure the tubing is clear, make sure the injector/restrictor are clean & clear.

Oh...and congrats on your first flight!!! Be safe, get the squawks ironed out, and it only gets better from here...

So the nozzle cleaning instructions (Lycoming SI 1414) mentioned on page 361 of the Sky Ranch Engineering Manual are no longer available on the Lycoming site.

Other than taking it apart and cleaning it in Hoppes #9 and/or MEK, followed by an air blast, what else do I need to know?

-Geoff

[dan]

Originally Posted by Geoff

Other than taking it apart and cleaning it in Hoppes #9 and/or MEK, followed by an air blast, what else do I need to know?

Sounds about right to me. A visual inspection of the orifice of the injector/restrictor, and checking whatever you soak it in for crud, would confirm whether it was a bit on the clogged side.

Starting there, if nothing turns up with the injector & distro line, I'd try to rule out an instrumentation error -- confirming the problem doesn't "follow" the connection.

Those are probably the easiest things to check before going much deeper.

[grantcarruthers]

might try swopping out #1 with #4 when you pull #4 for cleaning. If the problem crops up on #1 you have your answer??

As far as instrumnet error goes, I'd guess not. The high egt is associated with a high cht on the same cylinder. 2 different sensors telling the same story.